1. Field of the Invention
The present invention relates to isolated polypeptides having protease activity, and the use of isolated polypeptides having protease activity in animal feed. It also relates to the use of isolated nucleic acid sequences encoding the proteases in the recombinant production of isolated polypeptides having protease activity and isolated nucleic acid sequences encoding the proteases. The invention also relates to nucleic acid constructs, vectors, and host cells, including plant and animal cells, comprising the nucleic acid sequences, as well as methods for producing and using the proteases, particularly using the proteases in animal feed.
2. Background of the Invention
In the use of proteases in animal feed (in vivo), and/or the use of such proteases for treating vegetable proteins (in vitro) it is noted that proteins are essential nutritional factors for animals and humans. Humans and livestock usually get the necessary proteins from vegetable protein sources. Important vegetable protein sources are e.g. oilseed crops, legumes and cereals.
When e.g. soybean meal is included in the feed of mono-gastric animals such as pigs and poultry, a significant proportion of the soybean meal is not digested efficiently (the apparent ileal protein digestibility in piglets, growing pigs and poultry such as broilers, laying hens and roosters is only around 80%).
The gastrointestinal tract of animals consists of a series of segments each representing different pH environments. In mono-gastric animals such as pigs and poultry and many types of fish, the stomach is strongly acidic with a pH potentially as low as 1-2, while the intestine has a more neutral pH of around 6-7. Apart from the stomach and intestine, poultry also have a crop preceding the stomach. The pH in the crop is mostly determined by the feed ingested and hence typically lies in the range of pH 4-6. Protein digestion by a protease may occur along the entire digestive tract, provided that the protease is active and survives the conditions in the digestive tract. Hence, proteases which are highly acid stable and so can survive in the gastric environment and at the same time are efficiently active at the broad range of physiological pH of the digestive tract in the target animal are especially desirable.
Since animal feed is often formulated in pelleted form, in which steam is applied in the pelleting process, it is also desirable that proteases used in animal feed are capable of remaining active after exposure to said steam treatment.
In order to produce a protease for industrial use, it is important that the protease is produced in high yields making the product available in sufficient quantities in order to be able to provide the protease at a favourable price.